1. Field of the Invention
This invention relates to assemblies and planar structures for use therein which are expandable into 3-D structures such as stents and devices for making the planar structures.
2. Background Art
The following references are noted hereinbelow:    [1] D. A. Leung et al., “Selection of Stents for Treating Iliac Arterial Occlusive Disease,” J. VASC. INTERV. RADIOL., Vol. 14, 2003, pp. 137-52.    [2] P. E. Andersen et al., “Carotid Artery Stenting,” J. INTERV. RADIOL., Vol. 13, No. 3, 1998, pp. 71-6.    [3] C. R. Rees, “Stents for Atherosclerotic Renovascular Disease,” J. VASC. INTERV. RADIOL., Vol. 10, No. 6, 1999, pp. 689-705.    [4] C. Pena et al., “Metallic Stents in the Biliary Tree,” MIN. INVAS. THER. & ALLIED TECHNOL., Vol. 8, No. 3, 1999, pp. 191-6.    [5] B. K. Auge et al., “Ureteral Stents and Their Use in Endourology,” CURR. OPIN. UROL., Vol. 12, No. 3, 2002, pp. 217-22.    [6] Y. P. Kathuria, “Laser Microprocessing of Stent for Medical Therapy,” PROC. IEEE MICROMECH. HUMAN SCI., 1998, pp. 111-14.    [7] K. Takahata et al., “Batch Mode Micro-Electro-Discharge Machining,” IEEE J. MICROELECTROMECH. SYS., Vol. 11, No. 2, 2002, pp. 102-10.    [8] K. Takahata et al., “Coronary Artery Stents Microfabricated from Planar Metal Foil: Design, Fabrication, and Mechanical Testing,” PROC. IEEE MEMS, 2003, pp. 462-5.    [9] J. C. Conti et al., “The Durability of Silicone Versus Latex Mock Arteries,” PROC. ISA BIOMED. SCI. INSTRUM. SYMP., Vol. 37, 2001, pp. 305-12.    [10] R. C. Hibberler, “Mechanics of Materials Third Edition.” PRENTICE-HALL, INC., 1997.    [11] S. N. David Chua et al., “Finite-Element Simulation of Stent Expansion,” J. MATERIALS PROCESSING TECHNOL., Vol. 120, 2002, pp. 335-40.    [12]. “Metals Handbook Ninth Edition,” Vol. 8 Mechanical Testing, AMERICAN SOCIETY FOR METALS, 1985.    [13] F. Flueckiger et al., “Strength, Elasticity, and Plasticity of Expandable Metal Stents: In-Vitro Studies with Three Types of Stress,” J. VASC. INTERV. RADIOL., Vol. 5, No. 5, 1994, pp. 745-50.    [14] R. Rieu et al., “Radial Force of Coronary Stents: A Comparative Analysis,” CATHETER. CARDIOVASC. INTERV., Vol. 46, 1999, pp. 380-91.    [15] For example: J. D. Lubahn et al., “Plasticity and Creep of Metals,” JOHN WILEY & SONS, 1961.    U.S. Pat. Nos. 6,624,377 and 6,586,699 are related to the present application.
Stents are mechanical devices that are chronically implanted into arteries in order to physically expand and scaffold blood vessels that have been narrowed by plaque accumulation. Although they have found the greatest use in fighting coronary artery disease, stents are also used in blood vessels and ducts in other parts of the body. These include iliac arteries [1], carotid arteries [2], renal arteries [3], biliary ducts [4] and ureters [5]. The vast majority of coronary stents are made by laser machining of stainless steel tubes [6], creating mesh-like walls that allow the tube to be expanded radially with a balloon that is inflated during the medical procedure, known as balloon angioplasty. This fabrication approach offers limited throughput and prevents the use of substantial resources available for fabricating planar microstructures.
Micro-electro-discharge machining (μEDM) is another option for cutting metal microstructures. This technique is capable of performing 3-D micromachining in any electrical conductor with sub-micron tolerance and surface smoothness. It has not been extensively used for stent production in the past because traditional μEDM that uses single electrodes with single pulse timing circuits often suffers from even lower throughput than the laser machining. However, it has been recently demonstrated that the throughput of μEDM can be vastly increased by using spatial and temporal parallelism, i.e., lithographically formed arrays of planar electrodes with simultaneous discharges generated at individual electrodes [7].